The present invention relates to threaded plastic bottle caps for use with bottles containing a carbonated beverages or a liquid under vacuum. The cap is particularly suited for bottles containing carbonated beverages. In the past bottle caps for liquids such as carbonated beverages have been constructed of metal. Typically, these caps have been secured to the bottle by crimping or by constructing the cap with a skirt portion and forming a thread in the skirt. Usually the thread is formed in place on the bottle neck, using the threaded neck of the bottle as a die. Each of these cap constructions includes a liner disposed inside the cap for effecting a seal with the bottle neck. Also with both constructions the cap is deformed while on the bottle neck to secure it to the bottle and assure proper sealing. This forming of the cap on the bottle tends to avoid any problems that might be incurred because of bottle defects, irregularities, or variations in size due to manufacturing tolerances.
More recently there has been some use of plastic caps for bottles containing carbonated beverages or liquids under vacuum. These plastic caps are constructed with preformed threads and secured onto the bottle by simply threading the cap onto the threaded neck of the bottle. Since no deforming of the cap is employed once the cap is on the bottle neck, tolerance variations in the bottle manufacturing or in the cap manufacturing can become critical as far as effecting a proper seal. The molding of plastic caps can be done with great accuracy. Also the molding of plastic bottles can be done with accuracy. With glass bottles however, the tolerance variations are quite large and with today's normal production techniques, one cannot be assured of having bottles with neck configurations of precise shape and size. Not only are bottle manufacturing tolerances quite wide for glass bottles, such bottles are subject to chipping and other damage during handling. These problems with tolerances and irregularities encountered with glass bottles have in turn made it difficult to construct a plastic cap which is capable of use with such bottles where the contents are a carbonated beverage or one being packaged under vacuum. In both situations it is essential that a complete seal be formed between the bottle and the cap in order to maintain the carbonation or vacuum condition inside the bottle.
Plastic bottle caps which have been constructed for use with glass bottles have been made with specific sealing members inside the cap for effecting a seal with the bottle and for accommodating irregularities or wide tolerances in the bottle neck configuration. U.S. Pat. No. 4,143,785 discloses a plastic cap construction particularly suited for glass containers in which the contents is to be maintained under vacuum. In order to accommodate bottles with variations in wall thickness at the neck, the cap is provided with two sealing flanges on its interior which are adapted to engage with the inside and outside edges at the top of the bottle neck. These flanges are constructed in such a way that they flex as the cap is screwed down onto the bottle neck. In this way they can accommodate variations in the wall thickness of the bottle neck and provide a linear seal along the inner and outer edges of the neck.
Plastic caps have also been constructed with internal sealing members in the form of plugs which are adapted to be inserted into the interior of the bottle neck and engage against the inner wall surface of the bottle neck. Constructions of this type are disclosed in U.S. Pat. No. 4,090,631 and U.S. Pat. No. 4,322,012. The primary sealing of these caps is effected by the plug member which is constructed to flex and thereby accommodate variations in bottle tolerances
Still another plastic cap construction for glass bottles is disclosed in U.S. Pat. No. 4,061,240. In this cap, a flexible sealing member is provided on the interior of the cap. The sealing member is itself provided with a series of annular rings adapted to seat on the top of the bottle neck. As the cap is screwed down onto the bottle neck, the flexible member positions itself on the top of the bottle neck. Final threading causes a support member disposed above this sealing member to engage the sealing member and press it, and more specifically the annular rings, tightly against the top of the bottle neck. To further assure sealing of the annular rings against the top of the bottle neck, spaces are provided in the upper support to permit the pressurized atmosphere to escape over the top of the sealing member where it can exert a downward pressure on it. This cap is quite complicated in its construction. Segmented support members are provided to mechanically push the sealing member against the top of the bottle and channels must be formed in the cap structure to permit the pressurized atmosphere to act against the sealing member. Also the sealing rings which actually engage against the top of the bottle neck provide only a limited area of contact and thus may not be capable of providing a complete seal in any situation where the top of the bottle neck contains irregularities in its surface.